Piston pumps can generate a significant amount of noise during conventional modes of operation. Increasingly stringent regulations that are designed to limit overall noise in the workplace have created a demand for piston pumps that operate at lower sound levels.
There are a number of ways by which piston pumps generate noise. For example, when piston pumps operate, rotating pistons draw in hydraulic fluid through an inlet slot, typically at atmospheric pressure. After the pumping chamber is closed to the inlet, the piston passes bottom dead center (BDC). As the piston moves back to top dead center, it pressurizes and discharges the fluid into the outlet. As the fluid in the pumping chamber is pressurized during the transition just after BDC, the hydraulic fluid reaches a particular chamber pressure, after which it is discharged through the outlet and into a hydraulic system having a particular system pressure. Overpressurization or underpressurization of the piston chamber relative to the hydraulic system has been identified as a source of noise in piston pumps. An overpressurized piston chamber produces a pressure “overshoot” upon opening to the outlet, producing an audible noise. Such noise can increase as the pressure difference between the piston chamber and the outlet increases. Piston chamber underpressurization may produce noise because the rate of pressure change within the piston chamber is abrupt, and the higher system pressure impacts into the piston chamber. Ideal system operation occurs at conditions where the chamber pressure is equal to system pressure such that the pressure overshoot is zero and the rate of pressure change within the piston chamber is low.
Conventional methods to reduce piston pump noise have been somewhat ineffectual. Some existing methods suggest changing the port plate timing in such hydraulic piston pumps in order to lower the noise emanating from its use. However, such proposals are not feasible in that loads placed on port plates during operation are usually extremely high. Such high loads make it nearly impossible to move or adjust the port plates during operation.
Other techniques have also been proposed. In one example, an axial piston pump includes relief grooves that gradually transition the pressure as a barrel port rotates to the open port plate port. Another approach utilizes solenoids to open and close auxiliary ports formed in the port plate. However, none of these approaches have resulted in effectively eliminating noise arising from such piston pumps.
As a result, it is desirable to provide, among other things, an improved piston pump.